VUNA Nährstoffrückgewinnung Technologien

Risiken bei der Verwendung von Urin

Urine and Fertiliser Quality

The foremost goals of urine treatment are the recovery of nutrients for beneficial use. However, the urine treatment processes must also ensure that the end-products are safe to use, provide adequate human and environmental health protection, and are of adequate quality to ensure optimal market value. Pathogens and pharmaceuticals could potentially impact the quality of end products.

Research activities:

Removing pharmaceuticals: The majority of pharmaceutical residues are excreted in the urine (and not the faeces). Hence, the separate collection of urine isolates pharmaceuticals and prevents them from entering the environment. Experiments showed that long-term storage is not sufficient to remove pharmaceuticals. Nevertheless, processes occurring during nitrification, are suitable to remove certain pharmaceuticals. Virtually all pharmaceuticals can be removed in an activated carbon filter.

Inactivating pathogens: Whereas some pathogens can be excreted in the urine, others are introduced from cross-contamination with faeces during urine collection. We evaluated the viability of representative pathogens during urine treatment. We observed partial disinfection through urine storage and nitrification. Distillation is assumed to eliminate all pathogens due to high temperatures. Research partner: Environmental Chemistry Laboratory at EPFL.

Aurin Flüssigdünger

Urin-Sammelnetze

eThekwini Water and Sanitation introduced urine-diverting toilets as a system to supply sanitation to unserved regions, where water is scarce and water-borne sewer systems are too costly. Therefore a cost-efficient and optimised urine collection approach is necessary to harvest the valuable nutrients in urine.

Research activities:

Optimising urine collection: We aim to make urine collection more cost efficient. Therefore, we implemented a pilot urine collection scheme to gain experiences and suggest improvements. Based on the evaluated costs, we are currently developing a business plan.

Performance Modelling: The entire system of urine collection, transport and decentralised treatment consists of a large number of interconnected elements (e.g. toilets, storage tanks, treatment reactors) which influence the overall system performance (e.g. pollution control, urban hygiene, fertilizer production). Using a combination of system analysis and mathematical modelling we identified critical elements, evaluated the value of particular measurement schemes and estimated the overall system performance.

Soziale und wirtschaftliche Aspekte von Trenntoiletten

The success of any sanitation programme depends on people's willingness to accept it. Urine-diverting toilets are still not well accepted by many. In order to increase acceptance, health and hygiene education is needed.

Research activities:

Social acceptance: We accompanied the introduction of the VUNA technologies with studies, which investigated the socio-cultural perceptions and factors influencing users’ acceptance.

Campaigning for health & hyigene: Based on our findings from the acceptance studies, we developed appropriate educational activities and awareness material, e.g. for households and schools.

Incentives for urine production: By giving urine a financial value, we tested how to increase toilet use, improve hygiene, reduce loss of valuable nutrients and augment household income for the poorest.

Business model: To better understand the value chain from urine to fertiliser, we analysed the various components of the nutrient recovery system with a business perspective.

Source-separated urine contains most of the excreted nutrients, which can be recovered by using nitrification to stabilize the urine before concentrating the nutrient solution with distillation. The aim of this study was to test this process combination at pilot scale. The nitrification process was efficient in a moving bed biofilm reactor with maximal rates of 930 mg N L−1 d−1. Rates decreased to 120 mg N L−1 d−1 after switching to more concentrated urine. At high nitrification rates (640 mg N L−1 d−1) and low total ammonia concentrations (1,790 mg NH4-N L−1 in influent) distillation caused the main primary energy demand of 71 W cap−1 (nitrification: 13 W cap−1) assuming a nitrogen production of 8.8 g N cap−1 d−1. Possible process failures include the accumulation of the nitrification intermediate nitrite and the selection of acid-tolerant ammonia-oxidizing bacteria. Especially during reactor start-up, the process must therefore be carefully supervised. The concentrate produced by the nitrification/distillation process is low in heavy metals, but high in nutrients, suggesting a good suitability as an integral fertilizer.

In wastewater treatment, the rate of ammonia oxidation decreases with pH and stops very often slightly below a pH of 6. Free ammonia (NH3) limitation, inhibition by nitrous acid (HNO2), limitation by inorganic carbon or direct effect of high proton concentrations have been proposed to cause the rate decrease with pH as well as the cessation of ammonia oxidation. In this study, we compare an exponential pH term common for food microbiology with conventionally applied rate laws based on Monod-type kinetics for NH3 limitation and non-competitive HNO2 inhibition as well as sigmoidal pH functions to model the low pH limit of ammonia oxidizing bacteria (AOB). For this purpose we conducted well controlled batch experiments which were then simulated with a computer model. The results showed that kinetics based on NH3 limitation and HNO2 inhibition can explain the rate decrease of ammonia oxidation between pH 7 and 6, but fail in predicting the pH limit of Nitrosomonas eutropha at pH 5.4 and rates close to that limit. This is where the exponential pH term becomes important: this term decreases the rate of ammonia oxidation to zero, as the pH limit approaches. Previously proposed sigmoidal pH functions that affect large pH regions, however, led to an overestimation of the pH effect and could therefore not be applied successfully. We show that the proposed exponential pH term can be explained quantitatively with thermodynamic principles: at low pH values, the energy available from the proton motive force is too small for the NADH production in Nitrosomonas eutropha and related AOB causing an energy limited state of the bacterial cell. Hence, energy limitation and not inhibition or limitation of enzymes is responsible for the cessation of the AOB activity at low pH values.

Estimation of nitrite in source-separated nitrified urine with UV spectrophotometry

Monitoring of nitrite is essential for an immediate response and prevention of irreversible failure of decentralized biological urine nitrification reactors. Although a few sensors are available for nitrite measurement, none of them are suitable for applications in which both nitrite and nitrate are present in very high concentrations. Such is the case in collected source-separated urine, stabilized by nitrification for long-term storage. Ultraviolet (UV) spectrophotometry in combination with chemometrics is a promising option for monitoring of nitrite. In this study, an immersible in situ UV sensor is investigated for the first time so to establish a relationship between UV absorbance spectra and nitrite concentrations in nitrified urine. The study focuses on the effects of suspended particles and saturation on the absorbance spectra and the chemometric model performance. Detailed analysis indicates that suspended particles in nitrified urine have a negligible effect on nitrite estimation, concluding that sample filtration is not necessary as pretreatment. In contrast, saturation due to very high concentrations affects the model performance severely, suggesting dilution as an essential sample preparation step. However, this can also be mitigated by simple removal of the saturated, lower end of the UV absorbance spectra, and extraction of information from the secondary, weaker nitrite absorbance peak. This approach allows for estimation of nitrite with a simple chemometric model and without sample dilution. These results are promising for a practical application of the UV sensor as an in situ nitrite measurement in a urine nitrification reactor given the exceptional quality of the nitrite estimates in comparison to previous studies.

Remmele, A. (2013) The influence of anode material and current density on the emissions of disinfection by-products (DBPs) during electrolytic treatment of stored urine, 42 p, Institutional Repository

Complete nutrient recovery from source-separated urine by nitrification and distillation

In this study we present a method to recover all nutrients from source-separated urine in a dry solid by combining biological nitrification with distillation. In a first process step, a membrane-aerated biofilm reactor was operated stably for more than 12 months, producing a nutrient solution with a pH between 6.2 and 7.0 (depending on the pH set-point), and an ammonium to nitrate ratio between 0.87 and 1.15 gN gN−1. The maximum nitrification rate was 1.8 ± 0.3 gN m−2 d−1. Process stability was achieved by controlling the pH via the influent. In the second process step, real nitrified urine and synthetic solutions were concentrated in lab-scale distillation reactors. All nutrients were recovered in a dry powder except for some ammonia (less than 3% of total nitrogen). We estimate that the primary energy demand for a simple nitrification/distillation process is four to five times higher than removing nitrogen and phosphorus in a conventional wastewater treatment plant and producing the equivalent amount of phosphorus and nitrogen fertilizers. However, the primary energy demand can be reduced to values very close to conventional treatment, if 80% of the water is removed with reverse osmosis and distillation is operated with vapor compression. The ammonium nitrate content of the solid residue is below the limit at which stringent EU safety regulations for fertilizers come into effect; nevertheless, we propose some additional process steps that will increase the thermal stability of the solid product.

Technologies for the treatment of source-separated urine in the eThekwini Municipality

In recent years, a large number of urine-diverting dehydration toilets (UDDTs) have been installed in eThekwini to ensure access to adequate sanitation. The initial purpose of these toilets was to facilitate faeces drying, while the urine was diverted into a soak pit. This practice can lead to environmental pollution, since urine contains high amounts of nutrients. Instead of polluting the environment, these nutrients should be recovered and used as fertiliser. In 2010 the international and transdisciplinary research project VUNA was initiated in order to explore technologies and management methods for better urine management in eThekwini. Three treatment technologies have been chosen for the VUNA project. The first is struvite precipitation, a technology which has already been tested in multiple projects on urine treatment. Struvite precipitation is a simple and fast process for phosphorus recovery. Other nutrients, such as nitrogen and potassium, remain in the effluent and pathogens are not completely inactivated. Therefore, struvite precipitation has to be combined with other treatment processes to prevent environmental pollution and hygiene risks. The second process is a combination of nitrification and distillation. This process combination is more complex than struvite precipitation, but it recovers all nutrients in one concentrated solution, ensures safe sanitisation and produces only distilled water and a small amount of sludge as by-products. The third process is electrolysis. This process could be used for very small on-site reactors, because conversion rates are high and the operation is simple, as long as appropriate electrodes and voltages are used. However, nitrogen is removed and not recovered and chlorinated by-products are formed, which can be hazardous for human health. While urine electrolysis requires further research in the laboratory, struvite precipitation and nitrification/distillation have already been operated at pilot scale.

Removal rates and energy demand of the electrochemical oxidation of ammonia and organic substances in real stored urine

The separate collection and treatment of urine allows for an environmentally friendly and cost-efficient management of the nutrients contained in urine. The primary goal should be to recover all these nutrients. However, in some cases it will be economically or ecologically more sensitive to recover only the phosphorus, while nitrogen is removed together with organic substances (measured as chemical oxygen demand, COD) and pathogens. In this study, we investigated the use of galvanostatic electrolysis for the removal of nitrogen and COD from real stored urine. Non-active type boron-doped diamond (BDD) and active type thermally decomposed iridium oxide film (TDIROF) anodes were evaluated using batch experiments. On both anodes, ammonia was exclusively removed by indirect oxidation with active chlorine (AC: Cl2, HClO, and ClO−). As a consequence, ammonia was not completely removed, if chlorine was consumed by competing processes. While COD was present, ammonia removal was faster on TDIROF (227 ± 16 gN m−2 d−1 at 20 mA cm−2) than on BDD (43 ± 20 gN m−2 d−1 at 20 mA cm−2). The reason for the slower ammonia removal on BDD was the enhanced reaction of AC with organic molecules. In fact, hydroxyl radicals broke organic molecules down to shorter chain molecules which reacted with most of the AC leaving only little AC for the oxidation of ammonia. This preferential oxidation of organics resulted in very high COD removal rates on BDD (above 420 gCOD m−2 d−1 at 20 mA cm−2 for COD concentrations above 1000 mgCOD L−1). A main drawback of electrolysis with both anodes was the high energy demand (BDD: 55 W h gCOD−1 and 766 W h gN−1 for 90% and 6% removal, respectively. TDIROF: 67 W h gCOD−1 and 77 W h gN−1 for 30% and 40% removal. All at 20 mA cm−2). It can be concluded that BDD and TDIROF anodes could be combined in series for a fast, complete, and more energy efficient electrochemical urine treatment: COD could be removed on BDD before the residual ammonia would be removed on TDIROF.

Direct electrochemical oxidation of ammonia on graphite as a treatment option for stored source-separated urine

Electrolysis can be a viable technology for ammonia removal from source-separated urine. Compared to biological nitrogen removal, electrolysis is more robust and is highly amenable to automation, which makes it especially attractive for on-site reactors. In electrolytic wastewater treatment, ammonia is usually removed by indirect oxidation through active chlorine which is produced in-situ at elevated anode potentials. However, the evolution of chlorine can lead to the formation of chlorate, perchlorate, chlorinated organic by-products and chloramines that are toxic. This study focuses on using direct ammonia oxidation on graphite at low anode potentials in order to overcome the formation of toxic by-products. With the aid of cyclic voltammetry, we demonstrated that graphite is active for direct ammonia oxidation without concomitant chlorine formation if the anode potential is between 1.1 and 1.6 V vs. SHE (standard hydrogen electrode). A comparison of potentiostatic bulk electrolysis experiments in synthetic stored urine with and without chloride confirmed that ammonia was removed exclusively by continuous direct oxidation. Direct oxidation required high pH values (pH > 9) because free ammonia was the actual reactant. In real stored urine (pH = 9.0), an ammonia removal rate of 2.9 ± 0.3 gN·m−2·d−1 was achieved and the specific energy demand was 42 Wh·gN−1 at an anode potential of 1.31 V vs. SHE. The measurements of chlorate and perchlorate as well as selected chlorinated organic by-products confirmed that no chlorinated by-products were formed in real urine. Electrode corrosion through graphite exfoliation was prevented and the surface was not poisoned by intermediate oxidation products. We conclude that direct ammonia oxidation on graphite electrodes is a treatment option for source-separated urine with three major advantages: The formation of chlorinated by-products is prevented, less energy is consumed than in indirect ammonia oxidation and readily available and cheap graphite can be used as the electrode material.

Inhibition of direct electrolytic ammonia oxidation due to a change in local pH

Electrochemical ammonia oxidation has gained a lot of attention recently as an efficient method for ammonia removal from wastewater, for the use in ammonia-based fuel cells and the production of high purity hydrogen. Thermally decomposed iridium oxide films (TDIROF) have been shown to be catalytically active for direct ammonia oxidation in aqueous solutions if NH3 is present. However, the process was reported to be rapidly inhibited on TDIROF. Herein, we show that this fast inhibition of direct ammonia oxidation does not result from surface poisoning by adsorbed elemental nitrogen (Nads). Instead, we propose that direct ammonia oxidation and oxygen evolution can lead to a drop of the local pH at the electrode resulting in a low availability of the actual reactant, NH3. The hypothesis was tested with cyclic voltammetry (CV) experiments on stagnant and rotating disk electrodes (RDE). The CV experiments on the stagnant electrode revealed that the decrease of the ammonia oxidation peaks was considerably reduced by introducing an idle phase at open circuit potential between subsequent scans. Furthermore, the polarization of the TDIROF electrode into the hydrogen evolution region (HER) resulted in increased ammonia oxidation peaks in the following anodic scans which can be explained with an increased local pH after the consumption of protons in the HER. On the RDE, the ammonia oxidation peaks did not decrease in immediately consecutive scans. These findings would not be expected if surface poisoning was responsible for the fast inhibition but they are in good agreement with the proposed mechanism of pH induced limitation by the reactant, NH3. The plausibility of the mechanism was also supported by our numerical simulations of the processes in the Nernstian diffusion layer. The knowledge about this inhibition mechanism of direct ammonia oxidation is especially important for the design of electrochemical cells for wastewater treatment. The mechanism is not only valid for TDIROF but also for other electrodes because it is independent of the electrode material.

Formation of chlorination byproducts and their emission pathways in chlorine mediated electro-oxidation of urine on active and nonactive type anodes

Chlorination byproducts (CBPs) are harmful to human health and the environment. Their formation in chlorine mediated electro-oxidation is a concern for electrochemical urine treatment. We investigated the formation of chlorate, perchlorate, and organic chlorination byproducts (OCBPs) during galvanostatic (10, 15, 20 mA·cm–2) electro-oxidation of urine on boron-doped diamond (BDD) and thermally decomposed iridium oxide film (TDIROF) anodes. In the beginning of the batch experiments, the production of perchlorate was prevented by competing active chlorine and chlorate formation as well as by direct oxidation of organic substances. Perchlorate was only formed at higher specific charges (>17 Ah·L–1 on BDD and >29 Ah·L–1 on TDIROF) resulting in chlorate and perchlorate being the dominant CBPs (>90% of initial chloride). BDD produced mainly short chained OCBPs (dichloromethane, trichloromethane, and tetrachloromethane), whereas longer chained OCBPs (1,2-dichloropropane and 1,2-dichloroethane) were more frequently found on TDIROF. The OCBPs were primarily eliminated by electrochemical stripping: On BDD, this pathway accounted for 40% (dichloromethane) to 100% (tetrachloromethane) and on TDIROF for 90% (1,2-dichloroethane) to 100% (trichloromethane) of what was produced. A post-treatment of the liquid as well as the gas phase should be foreseen if CBP formation cannot be prevented by eliminating chloride or organic substances in a pretreatment.

Risiken bei der Verwendung von Urin

Pathogens and pharmaceuticals in source-separated urine in eThekwini, South Africa

In eThekwini, South Africa, the production of agricultural fertilizers from human urine collected from urine-diverting dry toilets is being evaluated at a municipality scale as a way to help finance a decentralized, dry sanitation system. The present study aimed to assess a range of human and environmental health hazards in source-separated urine, which was presumed to be contaminated with feces, by evaluating the presence of human pathogens, pharmaceuticals, and an antibiotic resistance gene. Composite urine samples from households enrolled in a urine collection trial were obtained from urine storage tanks installed in three regions of eThekwini. Polymerase chain reaction (PCR) assays targeted 9 viral and 10 bacterial human pathogens transmitted by the fecal–oral route. The most frequently detected viral pathogens were JC polyomavirus, rotavirus, and human adenovirus in 100%, 34% and 31% of samples, respectively. Aeromonas spp. and Shigella spp. were frequently detected gram negative bacteria, in 94% and 61% of samples, respectively. The gram positive bacterium, Clostridium perfringens, which is known to survive for extended times in urine, was found in 72% of samples. A screening of 41 trace organic compounds in the urine facilitated selection of 12 priority pharmaceuticals for further evaluation. The antibiotics sulfamethoxazole and trimethoprim, which are frequently prescribed as prophylaxis for HIV-positive patients, were detected in 95% and 85% of samples, reaching maximum concentrations of 6800 μg/L and 1280 μg/L, respectively. The antiretroviral drug emtricitabine was also detected in 40% of urine samples. A sulfonamide antibiotic resistance gene (sul1) was detected in 100% of urine samples. By coupling analysis of pathogens and pharmaceuticals in geographically dispersed samples in eThekwini, this study reveals a range of human and environmental health hazards in urine intended for fertilizer production. Collection of urine offers the benefit of sequestering contaminants from environmental release and allows for targeted treatment of potential health hazards prior to agricultural application. The efficacy of pathogen and pharmaceutical inactivation, transformation or removal during urine nutrient recovery processes is thus briefly reviewed.

Inactivation kinetics and mechanisms of viral and bacterial pathogen surrogates during urine nitrification

This paper assesses the inactivation performance and mechanisms in urine nitrification reactors using bacteria and bacteriophages as surrogates for human pathogens. Two parallel continuous-flow moving bed biofilm reactors (MBBRs) were operated over a two-month period. One MBBR was used to conduct a continuous spike experiment with bacteriophage MS2. The second reactor provided the matrix for a series of batch experiments conducted to investigate the inactivation of Salmonella typhimurium, Enterococcus spp., MS2, Qβ, and ΦX174 during urine nitrification. The roles of aeration, biological activity, and solution composition in inactivation were evaluated. Whereas bacteriophages ΦX174 and MS2 remained infective following urine nitrification, partial inactivation of bacteriophage Qβ was observed. Qβ inactivation was attributed primarily to aeration with a potential additive effect of biological processes, i.e., processes that are attributable to the presence of other microorganisms such as sorption to biomass, predation or enzymatic activity. Tailing of Qβ inactivation to a plateau indicated a protective effect of the solution components in aerated nitrification reactors. In contrast to the bacteriophages, S. typhimurium and Enterococcus spp. were mainly affected by biological processes: they were inactivated in biologically active nitrification reactors while remaining stable in chemically equivalent filtered controls. The tested bacteria could, for example, be out-competed by other microbial communities or sorbed to biomass in the reactor. Microbial communities did not adapt to inactivate bacteriophage MS2 (e.g., via increased prevalence of virus predators) in the experimental time-scale evaluated, with no observed inactivation of MS2 during continuous input for 51 days in the flow-through MBBR. The compilation of these results suggests that biological nitrification as a fertilizer production process remains insufficient as a stand-alone technology for the sanitization of source-separated urine.

Ammonia as an in situ sanitizer: inactivation kinetics and mechanisms of the ssRNA virus MS2 by NH3

Sanitizing human and animal waste (e.g., urine, fecal sludge, or grey water) is a critical step in reducing the spread of disease and ensuring microbially safe reuse of waste materials. Viruses are particularly persistent pathogens and can be transmitted through inadequately sanitized waste. However, adequate storage or digestion of waste can strongly reduce the number of viruses due to increases in pH and uncharged aqueous ammonia (NH3), a known biocide. In this study we investigated the kinetics and mechanisms of inactivation of the single-stranded RNA virus MS2 under temperature, pH and NH3 conditions representative of waste storage. MS2 inactivation was mainly controlled by the activity of NH3 over a pH range of 7.0–9.5 and temperatures lower than 40 °C. Other bases (e.g., hydroxide, carbonate) additionally contributed to the observed reduction of infective MS2. The loss in MS2 infectivity could be rationalized by a loss in genome integrity, which was attributed to genome cleavage via alkaline transesterification. The contribution of each base to genome transesterification, and hence inactivation, could be related to the base pKa by means of a Bronsted relationship. The Bronsted relationship in conjunction with the activity of bases in solution enabled an accurate prediction of MS2 inactivation rates.

Fate of the pathogen indicators phage ΦX174 and Ascaris suum eggs during the production of struvite fertilizer from source-separated urine

Human urine has the potential to be a sustainable, locally and continuously available source of nutrients for agriculture. Phosphate can be efficiently recovered from human urine in the form of the mineral struvite (MgNH4PO4·6H2O). However, struvite formation may be coupled with the precipitation of other constituents present in urine including pathogens, pharmaceuticals, and heavy metals. To determine if struvite fertilizer presents a microbiological health risk to producers and end users, we characterized the fate of a human virus surrogate (phage ΦX174) and the eggs of the helminth Ascaris suum during a low-cost struvite recovery process. While the concentration of phages was similar in both the struvite and the urine, Ascaris eggs accumulated within the solid during the precipitation and filtration process. Subsequent air-drying of the struvite filter cake partially inactivated both microorganisms; however, viable Ascaris eggs and infective phages were still detected after several days of drying. The infectivity of both viruses and eggs was affected by the specific struvite drying conditions: higher inactivation generally occurred with increased air temperature and decreased relative humidity. On a log–log scale, phage inactivation increased linearly with decreasing moisture content of the struvite, while Ascaris inactivation occurred only after achieving a minimum moisture threshold. Sunlight exposure did not directly affect the infectivity of phages or Ascaris eggs in struvite cakes, though the resultant rise in temperature accelerated the drying of the struvite cake, which contributed to inactivation.

Landwirtschaft

Urine contains about 50 % of the phosphorus (P) and about 90 % of the nitrogen (N) excreted by humans and is therefore an interesting substrate for nutrient recovery. Source-separated urine can be used to precipitate struvite or, through a newly developed technology, nitrified urine fertilizer (NUF). In this study, we prepared 33P radioisotope- and stable 15N isotope-labeled synthetic NUF (SNUF) and struvite using synthetic urine and determined P and N uptake by greenhouse-grown ryegrass (Lolium multiflorum var. Gemini) fertilized with these products. The P and N in the urine-based fertilizers were as readily plant-available in a slightly acidic soil as the P and N in reference mineral fertilizers. The ryegrass crop recovered 26 % of P applied with both urine-based fertilizers and 72 and 75 % of N applied as struvite and SNUF, respectively. Thus, NUF and urine-derived struvite are valuable N and P recycling fertilizers.

Urin-Sammelnetze

Distributed wastewater treatment is increasingly considered as an alternative to the predominantly transport based combination of sewer network and centralized wastewater treatment plant. If substantial amount of wastewater of a particular area is processed in small distributed treatment units, the sum of these units must be considered as one system providing an overall service. This paper focuses on the monitoring for centralized operation of such distributed units. We present a simple stochastic model to calculate probability distributions of process performance. We thereby simulated a fleet of simple treatment units with stochastic failure rates, unreliable sensors and regular routine inspections. All calculated performance indicators exhibit a considerable difference between the true performance and the perceived that is based on sensor observations. The results also show that there is a trade-off between investing into more reliable technology or into more frequent human interventions to achieve a certain performance. The simulations can quantify both effects and thereby support the identification of requirements for centralized monitoring of distributed treatment units. The model approach is generic and can be extended and applied to various distributed wastewater treatment technologies and contexts.

Distributed wastewater treatment is increasingly considered as an alternative to the predominantly transport based combination of sewer network and centralized wastewater treatment plant. If substantial amount of wastewater of a particular area is processed in small distributed treatment units, the sum of these units must be considered as one system providing an overall service. This paper focuses on the monitoring for centralized operation of such distributed units. We present a simple stochastic model to calculate probability distributions of process performance. We thereby simulated a fleet of simple treatment units with stochastic failure rates, unreliable sensors and regular routine inspections. All calculated performance indicators exhibit a considerable difference between the true performance and the perceived that is based on sensor observations. The results also show that there is a trade-off between investing into more reliable technology or into more frequent human interventions to achieve a certain performance. The simulations can quantify both effects and thereby support the identification of requirements for centralized monitoring of distributed treatment units. The model approach is generic and can be extended and applied to various distributed wastewater treatment technologies and contexts.

Soziale und wirtschaftliche Aspekte

The effect of giving respondents time to think in a choice experiment: a conditional cash transfer programme in South Africa

We conducted a choice experiment (CE) to estimate willingness to accept (WTA) values for a planned conditional cash transfer (CCT) programme designed to increase toilet use in South Africa. The payment is made conditional on using a toilet and bringing urine to a central collection point. In a split-sample approach, a segment of respondents were given time to think (TTT) (24 hours) about their responses, while the remaining respondents had to answer immediately. We found significant differences in the choice behaviour between the subsamples. To validate the stated preferences with actual behaviour, a CCT programme was implemented afterwards. The stated WTA estimates were far below those revealed by actual behaviour for both subsamples. Contrary to our expectations, the TTT group had underestimated their actual WTA values by an even larger margin. The preferences for various attributes were nevertheless useful in informing the design of the real intervention.

Tilley, E.; Logar, I.; Günther, I. (2017) The effect of giving respondents time to think in a choice experiment: a conditional cash transfer programme in South Africa, Environment and Development Economics, 22(2), 202-227, doi:10.1017/S1355770X16000280, Institutional Repository

The impact of conditional cash transfer on toilet use in eThekwini, South Africa

In the developing world, having access to a toilet does not necessarily imply use: infrequent or non-use limits the desired health outcomes of improved sanitation. We examine the sanitation situation in a rural part of South Africa where recipients of novel, waterless “urine-diverting dry toilets” are not regularly using them. In order to determine if small, conditional cash transfers (CCT) could motivate families to use their toilets more, we paid for urine via different incentive-based interventions: two were based on volumetric pricing and the third was a flat-rate payment (irrespective of volume). A flat-rate payment (approx. €1) resulted in the highest rates of regular (weekly) participation at 59%. The low volumetric payment (approx. €0.05/L) led to regular participation rates of only 12% and no increase in toilet use. The high volumetric payment (approx. €0.1/L) resulted in lower rates of regular participation (35%), but increased the average urine production per household per day by 74%. As a first example of conditional cash transfers being used in the sanitation sector, we show that they are an accepted and effective tool for increasing toilet use, while putting small cash payments in the hands of poor, largely unemployed populations in rural South Africa.

Cost-effectiveness and community impacts of two urine-collection programs in rural South Africa

As the number of technologies and programming approaches for improving global sanitation grows, there is an increasing need to evaluate the cost-effectiveness of each so that policy can be driven by informed decisions that consider cost as well as impact. I use data from two different urine-collection programs that were implemented in rural South Africa to model the cost-effectiveness of each in terms of the cost per litre of urine collected and the cost per household, over a range of operational values. One program was based on conditional cash transfers with the aim of increasing toilet use, while the second program was centrally managed and designed to be logistically simple for the municipality. In comparing the results of the two models I find a paradox. Urine that is collected from households by the municipality is less expensive than incentivized urine collection on both a volumetric and household basis, but only at urine collection rates that cannot be achieved without incentives. Conversely, the incentivized collection is more cost effective when the collection rates are low, but at rates that would correspond to very low incentive prices, rendering the incentive scheme useless. My results illustrate the importance of cost-effectiveness analysis as a tool in sanitation programming but I also highlight the need to view the data with a more nuanced approach that considers the complexities of program implementation in poor, rural communities as the mathematical optimal may not correspond to a realistic, or socially desirable one.

Tilley, E. (2016) Cost-effectiveness and community impacts of two urine-collection programs in rural South Africa, Environmental Science: Water Research and Technology, 2, 320-335/403, doi:10.1039/C5EW00237K, Institutional Repository

Data collection made easier?: Choosing between mobile phones and paper

Collecting field data is essential for Sandec’s research; yet, paper-based data can be difficult to collect and manage. Mobile phones offer advantages, but are not always the best option. This article looks at the ways mobile phones can help with water and sanitation-related data collection in low-income countries.

Mkhize, N. (2015) The role of health & hygiene education in the accept- ance, utilisation, and maintenance of urine diversion toilets in rural communities of KwaZulu-Natal (preliminary title). Master’s thesis, University of KwaZulu-Natal. In preparation.